A more thorough explanation:

The Orange Book is a list of patents for drugs or drug products that can be used by companies to make generic versions of those drugs. The list also includes the expiration dates of the patents. The official name of the Orange Book is Approved Drug Products with Therapeutic Equivalence Evaluations.

For example, let's say a company wants to make a generic version of a popular drug. They can look in the Orange Book to see if there is a patent on that drug and when it will expire. If the patent has already expired, they can go ahead and make the generic version. But if the patent is still in effect, they have two options. They can either wait until the patent expires before making the generic version, or they can challenge the validity of the patent.

The Orange Book is important because it helps companies know when they can legally make generic versions of drugs. This can help make drugs more affordable for people who need them.